Field of the Invention
The present invention relates to a printing apparatus that includes multiple sheet feed units and a discharge device with multiple discharge processing functions, and performs discharge processing control by means of sheet detection using an optical sensor in accordance with sheet information for which an instruction was given, and a post-processing apparatus.
Description of the Related Art
With a discharging apparatus, it is necessary to accurately detect the sheet position on a conveying route in a discharging apparatus in order to perform various discharge processing functions (shifting, folding, punching, saddle stitch stapling, etc.). In view of this, the discharging apparatus uses an optical sensor to detect the sheet position (includes detecting whether or not there is a sheet). Optical sensors are largely classified into a transmission type or a reflection type, the transmission type has the characteristic of having high position detection accuracy, and transmission-type optical sensors are used in discharging apparatuses. For this reason, in the case of using a type of sheet whose position cannot be detected with a transmission-type sensor, such as transparent film or an OHP sheet, for example, the sheet is only conveyed without position detection using an optical sensor being performed, and without the various discharge processing functions being carried out, and the sheet is discharged to the outside of the discharging apparatus. Japanese Patent Laid-Open No. 2002-274744 proposes controlling whether or not to execute discharge processing (shifting, folding, etc.) according to sheet type (sheet mass, OHP sheet, glossy sheet, colored paper, or sheet with holes).
However, the above-described conventional technique has the following problems. In a printing system such as POD (Print On Demand), compatibility with more types of media is desired. For example, there are also film sheets known as translucent film, which are not completely transparent but have a certain degree of transmittance as with OHP sheets, which are commonly recognized as being transparent, and these are used in printing. Because translucent film is not an OHP sheet, it is used in addition to discharge processing functions such as shifting, punching, and saddle stitching as a sheet type whose position can be detected by a transmission-type sensor.
However, among various commercially-available translucent films, there are sheets that are cloudy and are thought to have low transparency in terms of appearance, but are high in transparency in terms of optical properties and have properties close to those of OHP sheets. Since sheet position detection using a transmission-type sensor of a discharging apparatus cannot be performed when a translucent film having such properties is used and printing is executed with a sheet type of translucent film, it is always judged as an error in the discharging apparatus, and a state occurs in which discharge can never be performed.